Spark gap, apparatus therefor, and product thereof



Feb. 6, 1951 A. c. WALL ETAL 2,540,921

SPARK GAP, APPARATUS THE'REFOR, AND PRODUCT THEREOF MMM@ l INVENTORS Hlexanaer (i Walt BY Heie/ri (les Patented Feb. 6, 1951 SPARK GAP, APPARATUS THEREFOR, AND PRODUCT THEREOF Alexander C. Wall and Herbert E. Oles," Buffalo, N. Y., assignors to P. R. Mallory & Co., Inc., Indianapolis, 1nd., a corporation of Delaware Application November 17, 1949, Serial No. 127,934

The present' invention relates to spark'gaps oi the type used in high frequency ignition systems for converting currents of relatively low frequency into high frequency oscillations, to a novel method of making such spark gaps, and to an apparatus for carrying such method in practice.

In the co-pending application of A. C. Wall, Serial No. 549,278 filed on August 12, 1944 now Patent No. 2,459,855, for 'ignition System and Apparatus, there is disclosed a novel ignition systern for internal combustion engine including a source of low frequency electrical energy, an oscillating circuit including a spark gap and a condenser to convert the electrical energy to a high frequency current at relatively low voltage, and a transformer to convert the resulting low voltage high frequency energy to a relatively high voltage output for supply to a spark gap comprising a pair of spaced electrodes between which a discharge may take place. A constructional form of such a spark gap is disclosed in U. S. Patent 2,384,786 issued to Alexander C. Wall on August 1, 1944. The present application, moreover, is a division of co-pending application Serial No. 582,136 now Patent No. 2,491,631.

It is an object of the present invention to improve ignition systems of the described general character and more particularly to provide an improved spark gap structure therefor.

It is another object of the invention to provide means for making spark gaps wherein a pair f contact-bearing end plates are directly fixed and hermetically sealed together by means of an insulative spacer tube.

It is a further object of the invention to provide a simple, reliable and satisfactory method of assemblying a spark gap from its components whereby the desired exact spacing, concentricity and parallelism of the contact electrodes is positively assured.

It is also Within the contemplation of the invention to provide an apparatus for making spark gaps of the described type which is adapted to carry the method of the invention into practice.

The invention also contemplates a machine for making spark gaps which is simple in character and construction, and reliable in operation, and which permits the manufacture of spark gaps on a quantity production scale at a low cost.

Other and further objects and advantages of the invention Will become apparent from the following description, taken in conjunction With the accompanying drawings; in which Fig. 1 is a side elevational View of a machine for making spark gaps and embodying the principles of the present invention;

Fig. 2 is a fragmentary longitudinal sectional view of the gap-making machine, having parts in elevation, and drawn to a slightly larger scale;

Fig. 3 is a similar fragmentary sectional view showing the machine with the spark gap contact holders and the spacer tube fully assembled;

4 Claims. (C1. Z50-27.5)

Fig. 4 is a horizontal sectional view taken on line 4-4 of Fig. 3; and

Fig. 5 is a longitudinal sectional view of the finished spark gap, the size of the said spark gap being greatly exaggerated for reasons of clarity.

The construction of the spark gap embodying the invention Will be best understood by referring to Fig. 5. In this figure, reference numeral ID denotes an end plate formed of sheet metal in a generally circular shape and provided with an inwardly extending annular depression or recess II. The terminal region of end plate II) is provided With a generally U-shaped flange I2 opening in a direction opposite to that of recess II. In the center portion of the end plate there is formed a protuberance cr dimple I3 with an aperture I4 in the center thereof. In the finished form of the spark gap, the said aperture is closed by means of a glass bead I5 which is directly sealed to dimp-le I3 by means of a glass to metal seal.

To the inner face of end plate I0 there is secured a cup-shaped contact holder plate I 6 for example by having its ilange Il welded thereto at I8. The iiat center surface of contact holder plate I6 is likewise provided with an aperture I9 and has a contact 2E? seated thereon and secured thereto by means of welding or brazing. End plate Ill and preferably also contact holder IB are made of a metal which is adapted to be directly sealed to glass. Thus, end plates of chrome iron will readily seal to conventional soft or sodium glass, While plates made of a loWeX- pansion iron-base alloy containing 28-30% nickel, 15-18% cobalt and fractional percentages of manganese are easily sealed to conventional hard glass. Contact 20 may be made of any suitable metal, refractory metals, such as tungsten, being preferred. It Will be noted that end plate I0, and contact holder plate I6 define a closed space therebetween, a small aperture 2Ia being provided in the circumferential portion of the con-v tact holder plate in order to establish communication between said space and the space surrounding contact 28. 4

End plate I0, contact holder I6 and contact 20 constitute a contact assembly 2|, which is Spacedly mounted with another contact assembly of identical character, with the contacts 2E) concentric, parallel and closely spaced from each other. This spacing is assured by means of a spacer tube 22 of insulating material such as glass, having its ends seated in terminal flanges I2 of the respective end plates and directly sealed thereto, as this is indicated at 23, to provide a hermetically sealed spark gap construction.

It has been found that a spark gap of the desired construction provides excellent results and Will perform satisfactorily for very long periods of time. It has been also discovered, however, that the accurate concentricity, parallelism and spacing of contacts 20 is critically important for obtaining these results. The method and machine to be described hereinafter make it possible to obtain this critically important accuracy oi construction and spacing on a quantity production scale, without the use of highly skilled labor, and at a low cost.

Referring now more particularly to Figs. vl to 4 of the drawing, the machine of the invention comprises a frame 3l! which may be mounted on a suitable support or may be directly bolted or clamped to a work bench. A pair oi inachine ways 3l are secured to frame 30 and extend .in the vertical direction. Ylin these ways there is slidably arranged a sliding Vhead 32 which may be displaced in the vertical direction and may be clamped in any one of its adjusted positions by means of a locking screw 33 and wrench 34. Sliding head 32 carries a lead screw 35 capable of rotation by means of a hand wheel 35, thus providing for a small controlled movement of member 36u having a threaded portion 31 cooperating with the lead screw. Member 36a is provided with an internally threaded socket 38 adapted to receive and to hold a correspondingly threaded extension of an upper chuck 39. Chuck 39 comprises a downwardly extending cylindrical .sleeve 43 with longitudinal slots 4I therein defining three jaws ft2 which are externally urged by their resilient character and are adapted to engage annular depression il of contact end plate il).

Support 33 also carries a base plate 43 arranged in horizontal direction and having an aperture 44 therein.. This base plate is made of a ferromagnetic material, such as iron cr steel. Upon the apertured pcrtion of the base plate rests a permanent magnet i5 of an an nular shape which is securely held by the magnetic attraction between the said magnet and the base plate. Within magnet t5 there is mounted a lower chuck l5 having a construction closely similar to that of upper chuck 39 and having a plurality of longitudinal slots ft'i' deiining a plurality of gripping members or jaws 48 therein. Lower chuck 45 is secured to magnet by means of an interposed body cr mass 49 of a suitable ller material, such as a low melting point alloy composed or" 50% bismuth, 27% lead, 13% tin and 10% cadmium. It will be noted that the lower chuck may be adjusted in the horizontal position by simply sliding it in any direction and will be fixed in any one oi such positions by magnet 45.

The machine also includes high frequency heating means for applying heat to any desired portion or the spark gap assembly. These heat ing means are shown in the drawing in the form of a conductor loop 5t which may surround a portion of the spark gap assembly and is insulatedly supported in a sliding head 5|. Head 5l may be vertically displaced in ways 3l and may be fixed in its bolt 52 and wrench 53.

It has been found desirable to provide indicator means to indicate the relative position of the upper chuck with respect tc the lower chuck or the relative spacing of the contact assemblies carriedby such chucks. .A convenient form oisuch indicator means is shown in the drawing and comprises a horizontal arm 54 clamped to the upper chuck holding member iiia and carrying a downwardly extending indicator rod 55. It will be noted that the position or arm 54 on element 33a and the effective vlength of rod 55 may be adjusted and fixed by means adjusted position by lock' of set screws 5B and 51, respectively. The lower end of indicator rod 55 is adapted to engage actuating button 58 of dial indicator 59, which is likewise supported on base plate 43. In view of the fact that this dial indicator is of conventional construction and is well known to those skilled in the art, no detailed description thereof will be necessary.

From the foregoing description the operation `of the apparatus and the method of the invention will be readily understood. Referring to Figs. l to 3, an upper contact assembly 2| comprising an end plate IIJ, a contact holding member [6, a contact 2'0 and a short-length of glass tube 60 sealed to the end plate, is placed in the upper chuck by slightly compressing the upper chuck jaws and releasing them when the contact assembly is in place. The gripping surlaces of the jaws will engage the side walls of depression Il in the end plate and will securely hold the assembly. This operation places 'the upper contact face in a roughly horizontal direction, and is carried out when sliding head 32 is at the limit oi its upward travel. The lower contact assembly 2|/ of identical construction is similarly placed in the lower chuck and gas tube 6i is placed over the end of the glass tube 62 of the lower conduct assembly. It will be noted that tube 62 is directly sealed to the end plate of the lower' assembly and is considerably longer than the corresponding glass tube 60 so that it extends through opening 44 in base plate 43. Sliding head locking wrench 34 is now released and '32 dropped until the contacts are approximately three-fourths of an inch apart. vThis distance is not critical and in general will be determined by the dimensions of the spark gap to be made. The sliding head is then locked to the base.

By rotating Ythe lead screw hand wheel 36, the contacts 20 are now brought to a short distance, such as to of an inch from one another. 'This is desirable in order to facilitate observation of the relative position of the two contacts and their alignment into approximately concentric position. The Vlower chuck 46 is now Aslid yaround on the lower base 43 made of magnetic metal, until the two contacts are approximately concentric. The magnetic attraction between permanent magnet 45 and base plate 43 will positively maintain this horizontal adjustment of `the lower chuck. The upper chuck 40 is now compressed, which permits the upper contact to fall and rest on the lower contact in `such a `position that the two Contact faces vare in surface engagement and 'obviously parallel. At this time the upper chuck is released Aand `this once )more rigidly attaches the upper contact to the machine, with the upper vcontact face exactly parallel to the lower contact face (Fig. 2), vDuring this opera-A tion it may be necessary to VVlower the upper chuck by means of the rotating lead `screw 35 after the contact has been released until it 'is in such a position that the chuck jaws will again engage with recess Il provided for them inthe contact assembly. The upper Contact is noW raised va short distance, such as approximately .015 inches and, if necessary, the lower chuck, which carries the lower contact assembly, is adjusted so that once more the contacts are concentric. This may be desirable to correct any accidental changes in the alignment of the contacts that may have `been caused as a result of the upper contact assembly being released Afrom and being reengaged by the chuck jaws.

By means of the rotating lead screw, the upper contact is now moved in the upward direction for a distance suflicient for insertion of the glass spacer tube 22 between the upper and lower contact assemblies, such as approximately one inch. Glass spacer tube 22 is placed in recess l2 provided for it on the lower contact assembly. The upper contact assembly is now brought down until its recess l2 just touches the upper edge of spacer tube 22 (Fig. 3). A valve (not shown) is now opened to permit a iiow of hydrogen through the gas tube 6I. r)The gas passing through glass tube 62 obviously will illl the space between the two contacts and will escape around the upper end of the glass spacer tube and through the gas escape holes 2id provided in the upper contact assembly and contact tube 60.

The induction heater coil 50 is now displaced by loosening wrench 53 until the coil is positioned slightly below the lower contact and the high frequency heater is turned on. The lower contact assembly is brought up to glass sealing temperature at which point the upper contact assembly is moved downward by means of the rotating lead screw, pushing the glass spacer tube into recess l2 of the lower contact end plate and producing a glass seal of the spacer tube to said plate at 23. It will be noted that the hydrogen will now be burning.

Upon completion of the lower seal, induction heater coil 50 is moved upward to a position slightly above the upper contact and is xed in such position. The upper contact assembly including its end plate, will soon rise to glass sealing temperature. When such temperature has been obtained, the upper contact assembly is moved in the downward direction by means of the rotating lead screw and is caused to seal to 'the glass. With the heat still on, the upper contact is brought down farther until it is in face to face engagement with the lower contact. At this time the upper contact should be in surface engagement, parallel and concentric with the lower contact.

At this point in the operation, the reading on the dial indicator 59 is noted. The induction heater is now turned off and, by means of the rotating lead screw, the upper contact is moved in the upward direction to the predetermined spacing and is stopped when the desired spacing is read on the dial indicator. The upper chuck is now held manually in that position until the glass and metal in the upper chuck have cooled below the flow point of the glass. The upper chuck is now released by compressing the chuck ngers and the chuck is withdrawn from the spark gap in the upward direction by means of the rotating lead screw.

The sliding head lock 34 is now released and the sliding head moved upward to the limit of its travel. At this point in the operation, we have an upper and a lower contact assembly sealed together by means of the glass spacer tube. The contact faces are spaced to the predetermined distance. They are exactly parallel and concentric and are permanently xed in such a position as a result of the preceding operations. A stream of hydrogen is also passing through glass tube 62 and is burning at the upper end of the glass tube 60, which is sealed to the upper contact end plate.

An auxiliary torch (not shown) is now played on upper glass tube 60 and at the time the glass is about to close on itself, the gas valve is turned off, Continued heating on the said glass tube 6 produces a seal at that point. The lower chuck is released and the spark gap structure removed from the chuck. It is now ready for the nal processing which may include a suitable presparking treatment, lling the inner space of the spark gap with a substantially inert gaseous atmosphere, etc. Finally, glass tube 62 is cut off close to the lower end plate and its remaining portion sealed resulting in glass bead i5 of the finished spark gap structure illustrated in Fig. 5.

While the present invention, as to its objects and advantages, has been disclosed in connection with a preferred embodiment thereof, variations and modifications may be resorted to by those skilled in the art without departing` from the principles of the invention. All of these variations and modifications are considered to be within the true spirit and scope of the present invention, as disclosed in the foregoing description and defined by the appended claims.

What is claimed is:

1. A spark gap structure comprising in combination a pair of metal end plates bearing contact electrodes, and a spacer tube of fusible dielectric material, said tube having its terminal regions directly fused to corresponding regions of said plates to maintain said electrodes in predetermined spaced relation and to constitute therefor a hermetically sealed enclosure.

2. A spark gap structure comprising in combination a pair of circular metal end plates having a circumferential flange, a circular contact electrode mounted on each of said plates, a spacer tube of fusible vitreous dielectric material having its terminal regions conforming to said flanges of the plates, and a fused seal directly bonding said regions of the tube to the flanges of the plate to fix the electrodes in closely parallel-spaced concentric relation and to constitute therefor a hermetically sealed enclosure.

3. A spark gap structure comprising in combination a pair of circular end plates formed of sheet metal and having an annular circumferential flange, a cup-shaped contact holder member mounted on each of said end plates, a circular contact electrode on each of said holders, a glass spacer tube having its terminal regions secured to the flanges of said plates by means of a direct glass to metal hermetic seal to fix the said electrodes in closely parallel-spaced concentric relation and to constitute therefor a hermetically sealed enclosure, and an externally exposed annular depression in each of said end plates adapted to be engaged by a gripping mechanism.

4. A spark gap structure comprising in combination, a pair of metal plates, a pair of contact electrodes, means aixing an individual contact of said contact pair to an individual plate of said metal plates, and a tubular insulative spacing member having its ends fused to said plates for predeterminedly maintaining said electrodes in a definite spaced relationship.

ALEXANDER C. WALL. HERBERT E. OLES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,440,154 Oles Apr. 20, 1948 2,452,652 Hansen Nov. 2, 1948 2,478,119 Mitchel Aug. 2, 1949 

